Dynamic user interface and module facilitating content sharing in a distributed computing environment

ABSTRACT

A sharing client device shares content with viewing client devices. A sharing module operating on a sharing client device and on the viewing client devices facilitates the creation and analysis of viewer snapshots, permitting automatic determination of whether viewers are up-to-date with their display of shared content. Based on the analysis and on a policy of the sharing module, the sharing module can take a number of actions, such as generating and displaying a viewer summary that a user of the sharing client device may view to determine whether, or to what extent, the viewing client devices are up-to-date in their displays of the shared content.

FIELD OF ART

The present invention generally relates to the field of user interfaces,and more specifically, to methods and user interfaces for determining,reacting to, and summarizing whether viewers of content shared over adigital network are synchronized with respect to the sharer of thecontent.

BACKGROUND

Many users wish to share some or all of the contents of their computerscreens with others, such as when giving a presentation to others withina geographically distributed organization. However, factors such asnetwork latency may lead to lengthy (and possibly inconsistent) timesbefore a shared screen portion has been propagated to the screens ofothers with whom the portion is being shared. The problem isparticularly exacerbated in the case of wide geographic distributions,such as when the members of an organization are located on differentcontinents, which leads to greater network latency, and/or when thecontent requires more bandwidth, such as in the case of largehigh-resolution images. Accordingly, in many cases, those sharingportions of their screens (“sharers”) feel the need to pause and seekconfirmation from other sharing recipients (“viewers”) that they havereceived the latest updates. These pauses have various associateddisadvantages, such as the breaking of the flow of the sharer'snarrative, as well as the confusion inherent in the viewers trying toguess whether what they see is the same as what the sharer sees.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a detailed view of a computing environment in whichscreen portions are shared among different client devices, according toone embodiment.

FIG. 2 illustrates a user interface seen by a sharer when sharingcontent, according to one embodiment.

FIG. 3 is a block diagram illustrating sub-modules of the sharing moduleof FIG. 1, according to one embodiment.

FIG. 4 illustrates the interactions that take place between differententities of FIG. 1 when sharing content portions and summarizing viewerviews of the shared portions, according to one embodiment.

FIG. 5 is a high-level block diagram illustrating physical components ofa computer used as part or all of the client devices from FIG. 1,according to one embodiment.

The figures depict embodiments of the present invention for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated herein may be employed without departing fromthe principles of the invention described herein.

DETAILED DESCRIPTION

FIG. 1 illustrates a detailed view of a computing environment in whichscreen portions are shared among different client devices, according toone embodiment.

To address the problems inherent in screen sharing over a distributedcomputer network, each device involved in the sharing has a sharingmodule 140 that together provide to the sharer a graphical view of theshared content that is currently being displayed to the viewers. Thetechniques and user interfaces disclosed herein enable a sharer ofcontent, such as an employee giving a presentation over a distributednetwork, to readily determine whether viewers are up-to-date with theshared content. Alternatively and/or additionally, the sharing module140 of the sharer may automatically apply a policy on behalf of thesharer based on whether the viewers are up-to-date (e.g., haltingadvancing of a presentation if viewers are not up-to-date, or suggestingadvancing of a slide once the viewers all become up-to-date). Thiseliminates the need for the imprecise and disruptive pauses inherent inthe sharer explicitly asking viewers for confirmation of whether theysee the current content, allowing the presentation or other sharing toproceed more smoothly and naturally.

The sharing module 140 may be implemented in different manners indifferent embodiments. For example, in some embodiments, the sharingmodule 140 is implemented as a plugin or extension for a browser(s) usedby the sharer and viewer. In some embodiments, functionality of thesharing module 140 is implemented directly within application code of abrowser or other application (e.g., code implementing WebRTC), or inclient-side code of web pages performing the screen sharing (e.g.,JavaScript code making WebRTC calls). The implementations of the sharingmodule 140 may also differ on different client devices, such as anextension on the sharing client device 120, and within the browsers onthe viewing client devices 130. The sharing module 140 may also beimplemented in native clients of desktop operations, native mobileapplications of smartphones, or the like. The functionality of thesharing module 140 is described in additional detail below with respectto FIG. 3.

The client device 120 of the sharer, and the client devices 130 of theviewers, are computing devices such as smart phones, laptop computers,desktop computers, or any other devices supporting graphicalapplications (e.g., web browsers) capable of rendering graphical contenton the client devices. For the sake of simplicity, only one sharingclient device 120 and two viewing client devices 130 are illustrated inFIG. 1, although in practice there could be any number of each.

The network 150 may be any suitable communications network for datatransmission. In an embodiment such as that illustrated in FIG. 1, thenetwork 150 uses standard communications technologies and/or protocolsand can include the Internet. In another embodiment, the entities usecustom and/or dedicated data communications technologies.

FIG. 2 illustrates a user interface 200 seen by a sharer when sharingcontent, according to one embodiment. Region 205 includes a region 206containing content that is visually shared with the viewing users(hereinafter “shared portion”). For example, region 205 could be anapplication window managed by an application such as presentationsoftware, and region 206 could be the current slide displayed by thepresentation software. As another example, region 205 could be anapplication for a web browser playing a video, and region 206 could besome or all of the playing video. In some embodiments, region 206 mayalso be set to encompass the entire screen or the entirety of region205. Region 210 (e.g., a separate window) is generated by the sharingmodule 140 of the sharer's sharing client 120 and provides informationon the sharing of the shared content. For example, region 210 contains asnapshot 211 illustrating the shared content 206, and a region 212 withmetadata items 213-217, each describing a separate viewer. The exampleof FIG. 2 illustrates metadata items for three viewers havingidentifiers v:gxq21, v:gxq08, and v:hh52, respectively. The metadataitems also include the network address 214 from which the viewers arecommunicating with the sharer, the status 215 of the sharing of theshared content (e.g., “Decoding”, indicating that the viewers' clientdevices are in the process of rendering the shared content 206 receivedfrom the sharer over the network 150, or “Stalled” indicating that thenetwork is currently not properly delivering data), the amount 216 ofthe shared content that has been decoded (e.g., 20,971 bytes), and avisual snapshot 217 of the state of the shared content 206. Othermetadata 212 in some embodiments (not illustrated in FIG. 2) includeround trip time (measuring latency of data sent between the sharer andviewer), and/or a visual indicator of the general network qualitybetween the sharer and viewer (e.g., based on factors such as status 215and/or round trip time), such as an icon representing “good”,“acceptable”, or “poor.”

The sharer can look at the visual snapshot 217 for each viewer todetermine what image of the shared content is presently displayed on thescreen of the viewer. For example, in the example of FIG. 2, the sharercan glance at the snapshots 217A-217C (corresponding to the threeviewers) and determine that snapshot 217B of the second viewer isdifferent from the other snapshots (in that it displays content C1rather than C2), and (more importantly) different from the snapshot 211illustrating the current state of the shared content. The sharing module140 may visually emphasize a snapshot (such as 217B) differing from thecurrent state of the shared content (e.g., snapshot 211) to make iteasier for the sharer to identify the viewers whose shared content hasnot yet been synchronized with that of the sharer, such as with thehighlighting around snapshot 217B.

In some embodiments, the sharing module 140 includes within the visualsummary an indicator 218 summarizing viewers that are in sync or not insync with the sharer. For example, the indicator 218 in the example ofFIG. 2 notes that one of the three viewers is not currently in sync withthe sharer. This enables the sharer to make a quick determination ofwhether or not all viewers (or at least most viewers) are in sync, andtherefore (for example) whether the sharer should proceed to discuss theshared content. The visual summary may also include a special visualindication that all viewers are (or are not) in sync with the sharer,such as a change in color, or a temporary flash, when all the viewersbecome in sync with the sharer.

FIG. 3 is a block diagram illustrating sub-modules of the sharing module140, according to one embodiment.

In some embodiments, the sharing module 140 includes a propertiesinference module 305, which determines one or more properties of thesending of shared content from the sharer to the viewers.

For example, the properties inference module 305 may determine whichportion of the content displayed on the screen of the sharer to sharewith the viewers, rather than (or in addition to) relying on the sharerto specify the portion. For instance, rather than requiring the sharerto specify sharing of the entire screen, of a particular window, or of aportion of the window, the properties inference module 205 may analyzethe changing of the content displayed on the screen or within aparticular application window over time (e.g., analyzing degrees ofpixel changes across video frames), and based on the changesautomatically identify a particular frequently-changing portion of thescreen (e.g., a region in which presentation slides are displayed) anduse it as the shared portion after confirming with the sharer.

As another example, in some embodiments the properties inference module305 determines criteria defining a sharing trigger event for the sendingof the shared portion from the sharer to the viewers. For instance, thecriteria for the sending trigger event may be manually specified by theuser (e.g., some fixed number of milliseconds). Or the propertiesinference module 305 may infer a period of time as the criterion for thesending trigger event by analyzing the frequency of changes to theshared portion (e.g., an average period of time between changes) andsetting the period of time based on that frequency (e.g., sending theshared portion no more frequently than every 100 milliseconds). Theproperties inference module 305 may additionally and/or alternativelyconsider the content type of the shared content in the determination ofthe trigger, such as determining that the shared content is apresentation, and that therefore the trigger will be set based on thetypical time that a presentation slide is displayed, or that the triggerwill be set to a detectable event such as the transition from one slideto another. In other embodiments, there is no sending trigger event;rather, sending is performed automatically and continuously using avideo codec such as VP8, VP9, H.264, or H.265, e.g., in WebRTC, and thevideo codec streams the shared content to the viewing clients 130.

The sharing module 140 includes a content sending module 310 that sendsthe shared portion to viewers. In some embodiments, as noted above, thesending is performed continuously using a video codec, in which case thecontent sharing module 310 sends only indirectly, by initiating the useof the video codec (e.g., via use of a scripting language in a web pagein which the shared portion is located). In other embodiments, thecontent sending module 310 sends the shared portion only when thecriteria for the sending trigger event indicate to do so (e.g., afterthe lapse of a fixed sending period of time). In some embodiments, thecontent sending module 310 compares the current state of the sharedportion to the state of the shared portion that was most recently sent,refraining from sending the shared portion unless the current state andthat prior state differ by at least some given threshold amount. Thisconserves bandwidth by only sending data for sufficiently large changesthat would be noticeable by users. The content sending module 310 sendsthe data of the shared portion in different manners in differentembodiments, such as in unchanged form, or in a form that requires lessmemory, such as a lower-resolution form or a compressed form.

In some embodiments, the sharing module 140 includes an event capturemodule 315 that monitors occurrences of events that indicate that theshared portion may have been updated and hence require being sent againto the viewers. For example, the event capture module 315 may monitorthe detectable event, such as by using an application programminginterface (API) of an application in which the content is displayed(e.g., a presentation program) to register to receive notification ofsuch events, or by external monitoring of the application (e.g., byanalyzing pixels of the region corresponding to the application, such asidentifying degrees of pixel changes sufficiently large to indicate thatan entire slide was likely changed, or by identifying low-leveloperating system input events, such as keypresses, mouse clicks, orother user input events).

The sharing module 140 includes a snapshot comparison module 320 thatcompares snapshots received from viewers with the current state of theshared portion in order to determine whether the viewers aresynchronized or not with respect to the sharer. The snapshot comparisonmodule 320 may process the shared portion so that it is readilycomparable to the snapshots received from the viewers; e.g., if thesnapshots are in compressed form, the snapshot comparison module 320 maycompress the shared portion in a similar manner prior to comparing it tothe snapshots, so as to obtain equivalent images for comparison. Eachfailure of the snapshots received from one of the viewers to match thecurrent state of the shared portion indicates that that viewer is notsynchronized with respect to the sharer (that is, with respect to theshared portion displayed on the screen of the sharer). A snapshot isconsidered to match the current state of the shared portion, or to matchanother snapshot, if the visual similarity (e.g., pixel-wise similarity)of the snapshot to the shared portion or other snapshot is at least somethreshold level.

The sharing module 140 applies a policy to determine which actions totake in response to the determination of whether or not the viewers aresynchronized with respect to the sharer. Different possible actionstaken by the policy include those of a viewer summary generation module325 that generates a visual summary of the shared portion that variesaccording to the synchronization status of the various viewers, and anon-synchronization response module 330 that takes an action in responseto identifying one or more of the viewers that are not synchronized withrespect to the sharer.

The sharing module 140 includes a viewer summary generation module 325that generates a visual summary of the state of the shared portion ascurrently viewed by the various viewers. For example, the region 212 isone example of such a visual summary. In some embodiments, the viewersummary generation module 325 modifies the generation of the visualsummary based on a count of the viewers. For example, if there aresufficiently few viewers (e.g., fewer than some predetermined numbersuch as 7, or fewer than some function of the amount of available spacefor displaying the visual summary), then a visual summary such as region212 of FIG. 2 may be employed, showing a snapshot for each viewer, alongwith accompanying metadata. Otherwise, however, less information can bedisplayed in the interests of avoiding visual clutter. For instance, thevisual summary could contain a count derived from the number of viewersthat have a snapshot not matching that for the current shared portion(e.g., the number of viewers that are, or that are not, currently seeingthe shared portion), or a visual indication that all viewers are nowseeing the current shared portion (i.e., that the snapshots of all theviewers match the shared portion of the sharer), without showing thedetails of each viewer.

The sharing module 140 additionally includes a non-synchronizationresponse module 330 that takes an action in response to identifying oneor more of the viewers that are not synchronized with respect to thesharer. In some embodiments, the non-synchronization response module 330displays a visual indication to the sharer that the identified viewer(s)is not synchronized, such as by highlighting or otherwise visuallyemphasizing the username or other indication of the user within thevisual summary. In some embodiments, the non-synchronization responsemodule 330 modifies functionality (e.g., the user interface) of anapplication of the sharer that manages the shared portion so as toprevent further change to the shared portion, re-enabling the userinterface of the application after all (or some threshold number orpercentage of) the viewers are synchronized. For example, theapplication might be presentation software, and the non-synchronizationresponse module 330 might disable a portion of the user interface usedto advance to the next slide until all the viewers are synchronized.(Similarly, in some embodiments when all viewers are determined to besynchronized, the sharing module 140 automatically interacts with theapplication that produces the shared portion, such as automaticallyadvancing to the next slide of a presentation application, or promptingthe sharer to do so, or otherwise initiating updating of the sharedportion.) In some embodiments, the non-synchronization response module330 re-sends the shared portion to the identified viewers that are notin synchronization. In some embodiments, a video codec is designed ormodified to take the received snapshots into account when determiningwhen to send or re-send the shared portion, and is used to accomplishthe re-sending. In some embodiments, the non-synchronization responsemodule 330 determines, after some period of a particular viewer beingdetermined not to be synchronized with respect to the sharer, that theviewer is encountering sharing problems and accordingly removes thatviewer from determinations of whether the sharer should wait on accountof that viewer. For example, if the second viewer in the example of FIG.2 were determined to be encountering network problems, the visualsummary indication 218 could be revised to note instead that bothviewers that are not encountering network problems are in sync with thesharer, and thus the sharer should proceed with discussion, given thatwaiting for the remaining viewer likely does not make sense.

The sharing module 140 additionally includes a snapshot creation module355 used by client devices 130 of the viewers to generate snapshots ofthe shared content. In some embodiments, the snapshot creation module355 downsamples the shared portion (e.g., to 80×60 pixels) as receivedfrom the video decoder on the viewing client 130, then converts thedownsampled portion to another image format, such as JPEG. In someembodiments, the snapshot creation module 355 processes the sharedportion as stored in the video buffer of the viewing client 120 afterrendering, rather than directly processing the shared portion asreceived from the video decoder, before rendering. The snapshot creationmodule 355 may create and send snapshots to the sharer according todifferent schedules in different embodiments, such as at fixedone-second intervals. Alternatively, the snapshot creation module 355may first compare the last snapshot that it sent to the sharer with theshared portion currently displayed on the client (e.g., after firstreducing it to a new snapshot so as to be comparable with the lastsnapshot sent), and only send a new snapshot if the difference betweenthe two is above some threshold indicating that the image change wassufficiently large. As another alternative, the snapshot creation module355 may send a snapshot only in response to an explicit request from thesharing client 120. For example, the event capture module 315 might sendan explicit request to the viewing clients to send snapshots, afternoting the occurrence of an event leading to a change in the sharedcontent of the sharing client 120 (e.g., a slide change event) andsending the changed shared content.

As previously noted, the sharing module 140 may have differentfunctionality on the sharing client 120 and on the viewing clients 130.For example, in some embodiments the viewing clients 130 require lesssharing functionality than the sharing client 120, and hence the sharingmodules 140 on the viewing clients 130 have less functionality than thesharing module 140 on the sharing client 120. For example, the sharingmodule 140 of the sharing client 120 might include the propertiesinference module 305, the content sending module 310, the event capturemodule 315, the snapshot comparison module 320, the viewer summarygeneration module 325, and the non-synchronization response module 330,whereas the sharing module 140 of the viewing clients 130 might includeonly the snapshot creation module 355. Thus, in some embodiments, thesharing module 140 on the viewing clients (for example) may be extremelylightweight, e.g., implemented purely in a scripting language such asJavaScript within a web browser, without any need for plug-ins orextensions. This is particularly advantageous in environments in whichviewers lack permissions to install software on their own computingdevices.

FIG. 4 illustrates the interactions that take place between differententities of FIG. 1 when sharing content portions and summarizing viewerviews of the shared portions, according to one embodiment.

The sharer initiates 405 screen sharing on the sharing client device120. For example, in various embodiments the sharer may specify who theviewers will be, which portion of the screen to use as the sharedportion, and/or the like.

The sharing module 140 determines 410 sharing properties, e.g., asdiscussed above with respect to the properties inference module 305.

In some embodiments, the sharing module 140 detects 415 the occurrenceof a sharing trigger, such as a lapse of a given period of time, theoccurrence of a semantic event in an application encompassing the sharedportion, the occurrence of low-level event, or the like. The detectionmay be performed using the event capture module 315. In otherembodiments in which the sharing is performed continuously via a videocodec such as those in WebRTC, sharing triggers are not used.

The sharing module 140 sends 420 the shared portion to the clientdevices 130 of the viewers, as described above with respect to thecontent sending module 310. In embodiments in which sharing triggers areemployed, sending is performed in response to the occurrence of asharing trigger.

The sharing modules 140 of the various client devices 130 of the viewersgenerate 425 snapshots of the shared portion as currently displayed tothe viewers, and send the snapshots to the sharer, as described abovewith respect to the snapshot creation module 355.

The sharing module 140 of the sharing client device 120 determines 435whether viewers are synchronized with respect to the sharer based on thereceived snapshots. If any viewers are not synchronized, appropriateaction is taken, as described above with respect to thenon-synchronization module 330. For example, an indicator of a number ofviewers not synchronized can be shown to the sharer so that the sharercan decide whether or not to proceed with discussion of the sharedportion.

The sharing module 140 of the sharing client device 120 generates 440and displays a visual summary of the shared portions as viewed by theviewers (including visual indications of identified viewers that are notsynchronized with respect to the sharer, if any), as described abovewith respect to the viewer summary generation module 325.

FIG. 5 is a high-level block diagram illustrating physical components ofa computer 500 used as part or all of the client devices 120 or 130 fromFIG. 1, according to one embodiment. Illustrated are at least oneprocessor 502 coupled to a chipset 504. Also coupled to the chipset 504are a memory 506, a storage device 508, a graphics adapter 512, and anetwork adapter 516. A display 518 is coupled to the graphics adapter512. In one embodiment, the functionality of the chipset 504 is providedby a memory controller hub 520 and an I/O controller hub 522. In anotherembodiment, the memory 506 is coupled directly to the processor 502instead of the chipset 504.

The storage device 508 is any non-transitory computer-readable storagemedium, such as a hard drive, compact disk read-only memory (CD-ROM),DVD, or a solid-state memory device. The memory 506 holds instructionsand data used by the processor 502. The graphics adapter 512 displaysimages and other information on the display 518. The network adapter 516couples the computer 500 to a local or wide area network.

As is known in the art, a computer 500 can have different and/or othercomponents than those shown in FIG. 5. In addition, the computer 500 canlack certain illustrated components. In one embodiment, a computer 500acting as a server may lack a graphics adapter 512, and/or display 518,as well as a keyboard or pointing device. Moreover, the storage device508 can be local and/or remote from the computer 500 (such as embodiedwithin a storage area network (SAN)).

As is known in the art, the computer 500 is adapted to execute computerprogram modules for providing functionality described herein. As usedherein, the term “module” refers to computer program logic utilized toprovide the specified functionality. Thus, a module can be implementedin hardware, firmware, and/or software. In one embodiment, programmodules are stored on the storage device 508, loaded into the memory506, and executed by the processor 502.

Embodiments of the entities described herein can include other and/ordifferent modules than the ones described here. In addition, thefunctionality attributed to the modules can be performed by other ordifferent modules in other embodiments. Moreover, this descriptionoccasionally omits the term “module” for purposes of clarity andconvenience.

OTHER CONSIDERATIONS

The present invention has been described in particular detail withrespect to one possible embodiment. Those of skill in the art willappreciate that the invention may be practiced in other embodiments.First, the particular naming of the components and variables,capitalization of terms, the attributes, data structures, or any otherprogramming or structural aspect is not mandatory or significant, andthe mechanisms that implement the invention or its features may havedifferent names, formats, or protocols. Also, the particular division offunctionality between the various system components described herein ismerely for purposes of example, and is not mandatory; functionsperformed by a single system component may instead be performed bymultiple components, and functions performed by multiple components mayinstead performed by a single component.

Some portions of above description present the features of the presentinvention in terms of algorithms and symbolic representations ofoperations on information. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. These operations, while describedfunctionally or logically, are understood to be implemented by computerprograms. Furthermore, it has also proven convenient at times, to referto these arrangements of operations as modules or by functional names,without loss of generality.

Unless specifically stated otherwise as apparent from the abovediscussion, it is appreciated that throughout the description,discussions utilizing terms such as “determining” or “displaying” or thelike, refer to the action and processes of a computer system, or similarelectronic computing device, that manipulates and transforms datarepresented as physical (electronic) quantities within the computersystem memories or registers or other such information storage,transmission or display devices.

Certain aspects of the present invention include process steps andinstructions described herein in the form of an algorithm. It should benoted that the process steps and instructions of the present inventioncould be embodied in software, firmware or hardware, and when embodiedin software, could be downloaded to reside on and be operated fromdifferent platforms used by real time network operating systems.

The present invention also relates to an apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes, or it may comprise a general-purpose computerselectively activated or reconfigured by a computer program stored on acomputer readable medium that can be accessed by the computer. Such acomputer program may be stored in a non-transitory computer readablestorage medium, such as, but is not limited to, any type of diskincluding floppy disks, optical disks, CD-ROMs, magnetic-optical disks,read-only memories (ROMs), random access memories (RAMs), EPROMs,EEPROMs, magnetic or optical cards, application specific integratedcircuits (ASICs), or any type of computer-readable storage mediumsuitable for storing electronic instructions, and each coupled to acomputer system bus. Furthermore, the computers referred to in thespecification may include a single processor or may be architecturesemploying multiple processor designs for increased computing capability.

The algorithms and operations presented herein are not inherentlyrelated to any particular computer or other apparatus. Variousgeneral-purpose systems may also be used with programs in accordancewith the teachings herein, or it may prove convenient to construct morespecialized apparatus to perform the required method steps. The requiredstructure for a variety of these systems will be apparent to those ofskill in the art, along with equivalent variations. In addition, thepresent invention is not described with reference to any particularprogramming language. It is appreciated that a variety of programminglanguages may be used to implement the teachings of the presentinvention as described herein, and any references to specific languagesare provided for invention of enablement and best mode of the presentinvention.

The present invention is well suited to a wide variety of computernetwork systems over numerous topologies. Within this field, theconfiguration and management of large networks comprise storage devicesand computers that are communicatively coupled to dissimilar computersand storage devices over a network, such as the Internet.

Finally, it should be noted that the language used in the specificationhas been principally selected for readability and instructionalpurposes, and may not have been selected to delineate or circumscribethe inventive subject matter. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting, of the scopeof the invention, which is set forth in the following claims.

What is claimed is:
 1. A computer-implemented method for generating agraphical user interface indicating viewer states of content of a screenof a sharer visually shared with a plurality of viewers over adistributed network, the computer-implemented method comprising:identifying a shared portion of the screen content that is being sharedwith client devices of the plurality of viewers; receiving, from eachclient device of the plurality of viewers, a snapshot image generated onthe client device and corresponding to a state of the shared portioncurrently displayed on a screen of the client device; identifying, basedon a comparison of the received snapshot images and the shared portion,whether the viewers are synchronized with respect to the sharer; andapplying a policy based on whether the viewers are synchronized withrespect to the sharer, wherein applying the policy comprises displaying,using the received snapshot images, a visual summary of the sharedportion as currently displayed on screens of the plurality of viewers,the visual summary including a visual indication of identified viewersthat are not synchronized with respect to the sharer.
 2. Thecomputer-implemented method of claim 1, wherein applying the policycomprises: responsive to identifying, based on the received snapshotimages, at least a threshold number of viewers that are not synchronizedwith respect to the sharer: preventing further change to the sharedportion; determining, based on additional later-received snapshotimages, that all of the viewers are in synchronization with respect tothe sharer; and responsive to the determining, enabling further changesto the shared portion.
 3. The computer-implemented method of claim 1,wherein applying the policy comprises: responsive to identifying, basedon the received snapshot images, a viewer that is not synchronized withrespect to the sharer, re-sending the shared portion to the identifiedviewer.
 4. The computer-implemented method of claim 1, wherein applyingthe policy comprises: responsive to identifying, based on the receivedsnapshot images, that all the viewers are in synchronization withrespect to the sharer, initiating updating of the shared portion byinteracting with an application that produces the shared portion.
 5. Thecomputer-implemented method of claim 1, wherein displaying the visualsummary comprises including the snapshot images received from the clientdevices within the visual summary.
 6. The computer-implemented method ofclaim 1, wherein generating the visual summary comprises including, inthe visual summary, a count derived from a number of snapshot imagesmatching the shared portion.
 7. The computer-implemented method of claim1, wherein generating the visual summary comprises including, in thevisual summary, a visual indicator indicating that all the snapshotimages match the shared portion.
 8. A non-transitory computer-readablestorage medium containing executable instructions for generating agraphical user interface indicating viewer states of content of a screenof a sharer visually shared with a plurality of viewers over adistributed network, the instructions when executed by a computerprocessor performing actions comprising: identifying a shared portion ofthe screen content that is being shared with client devices of theplurality of viewers; receiving, from each client device of theplurality of viewers, a snapshot image generated on the client deviceand corresponding to a state of the shared portion currently displayedon a screen of the client device; identifying, based on a comparison ofthe received snapshot images and the shared portion, whether the viewersare synchronized with respect to the sharer; and applying a policy basedon whether the viewers are synchronized with respect to the sharer,wherein applying the policy comprises displaying, using the receivedsnapshot images, a visual summary of the shared portion as currentlydisplayed on screens of the plurality of viewers, the visual summaryincluding a visual indication of identified viewers that are notsynchronized with respect to the sharer.
 9. The non-transitorycomputer-readable storage medium of claim 8, wherein applying the policycomprises: responsive to identifying, based on the received snapshotimages, at least a threshold number of viewers that are not synchronizedwith respect to the sharer: preventing further change to the sharedportion; determining, based on additional later-received snapshotimages, that all of the viewers are in synchronization with respect tothe sharer; and responsive to the determining, enabling further changesto the shared portion.
 10. The non-transitory computer-readable storagemedium of claim 8, wherein applying the policy comprises: responsive toidentifying, based on the received snapshot images, a viewer that is notsynchronized with respect to the sharer, re-sending the shared portionto the identified viewer.
 11. The non-transitory computer-readablestorage medium of claim 8, wherein applying the policy comprises:responsive to identifying, based on the received snapshot images, thatall the viewers are in synchronization with respect to the sharer,initiating updating of the shared portion by interacting with anapplication that produces the shared portion.
 12. The non-transitorycomputer-readable storage medium of claim 8, wherein displaying thevisual summary comprises including the snapshot images received from theclient devices within the visual summary.
 13. The non-transitorycomputer-readable storage medium of claim 8, wherein generating thevisual summary comprises including, in the visual summary, a countderived from a number of snapshot images matching the shared portion.14. The non-transitory computer-readable storage medium of claim 8,wherein generating the visual summary comprises including, in the visualsummary, a visual indicator indicating that all the snapshot imagesmatch the shared portion.
 15. A computer system comprising: a computerprocessor; and executable instructions that when executed by thecomputer processor perform actions comprising: identifying a sharedportion of the screen content that is being shared with client devicesof the plurality of viewers; receiving, from each client device of theplurality of viewers, a snapshot image generated on the client deviceand corresponding to a state of the shared portion currently displayedon a screen of the client device; identifying, based on a comparison ofthe received snapshot images and the shared portion, whether the viewersare synchronized with respect to the sharer; and applying a policy basedon whether the viewers are synchronized with respect to the sharer,wherein applying the policy comprises displaying, using the receivedsnapshot images, a visual summary of the shared portion as currentlydisplayed on screens of the plurality of viewers, the visual summaryincluding a visual indication of identified viewers that are notsynchronized with respect to the sharer.
 16. The computer system ofclaim 15, wherein applying the policy comprises: responsive toidentifying, based on the received snapshot images, at least a thresholdnumber of viewers that are not synchronized with respect to the sharer:preventing further change to the shared portion; determining, based onadditional later-received snapshot images, that all of the viewers arein synchronization with respect to the sharer; and responsive to thedetermining, enabling further changes to the shared portion.
 17. Thecomputer system of claim 15, wherein applying the policy comprises:responsive to identifying, based on the received snapshot images, aviewer that is not synchronized with respect to the sharer, re-sendingthe shared portion to the identified viewer.
 18. The computer system ofclaim 15, wherein applying the policy comprises: responsive toidentifying, based on the received snapshot images, that all the viewersare in synchronization with respect to the sharer, initiating updatingof the shared portion by interacting with an application that producesthe shared portion.
 19. The computer system of claim 15, whereindisplaying the visual summary comprises including the snapshot imagesreceived from the client devices within the visual summary.
 20. Thecomputer system of claim 15, wherein generating the visual summarycomprises including, in the visual summary, a count derived from anumber of snapshot images matching the shared portion.
 21. Thecomputer-implemented method of claim 1, wherein receiving the snapshotimage comprises at least one of: receiving snapshot images from eachclient device at fixed time intervals; receiving the snapshot image fromeach client device based on a comparison between the snapshot image anda last snapshot image sent by the client device; receiving the snapshotimage from each client device in response to a request sent to theclient device.
 22. The computer-implemented method of claim 1, whereinidentifying whether the viewers are synchronized with respect to thesharer is based on a pixel-wise comparison of the received snapshotimages and the shared portion.
 23. The computer system of claim 15,wherein receiving the snapshot image comprises at least one of:receiving snapshot images from each client device at fixed timeintervals; receiving the snapshot image from each client device based ona comparison between the snapshot image and a last snapshot image sentby the client device; receiving the snapshot image from each clientdevice in response to a request sent to the client device.
 24. Thecomputer system of claim 15, wherein identifying whether the viewers aresynchronized with respect to the sharer is based on a pixel-wisecomparison of the received snapshot images and the shared portion.